yep, no problem.
Historical, blue pigments have been somewhat rarer and used as a symbol of wealth and royalty. The Egyptians used it for the high ranking and pharaohs as pigment on the gold to give the standard gold/blue scheme we think of with the pharaohs, this was Egyptian blue and believed to be one of the first synthetic pigments. It was a bit of stuff with copper and calcium but I can't say the full mix.. not my field ^_^ The Maya had there Maya Blue which was amazingly resistance to the elements as even the worse of weathered stuff, often has the blues unfaded.
During the more 'Medieval' area, the only real way they had of manually dying clothing blue, was using Woad. There are... theories that Woad was used for the Picts (the Pictured people) but the evidence is.. interestingly missing we know a group referred to be the Romans as painted or tattooed people, though the word used to describe the colour is more a blue/green which were pretty common at the time, and wouldn't really be what many of us would call Blue, it's just later on the term was applied to Blue (Vitrum isn't latin for Blue but glass, Woad is caustic so tattoo tests these days have been... poor and historical finds hint they used a copper base) (in the same way as in Japan, the word for Green and the word for Blue was the same until quite recently they created a new word for Green. This is why anyone that has watched Japanese animation and you see a traffic light which is Blue instead of green, it's kinda a hold back because of that. It was a mistake done soo long ago and soo often that it's kinda a cultural point now).
That said, what is known of Anglo-saxon clothing they would use a mixture between natural colours (of the wool and stuff) but also did some dying. Mostly, these were bad jobs and the more money you had, the better the dye job and colour. the Poor would have a bit uneven and a bit washed out over time, where the richer, the 'richer' the colour, which is why we see in art and samples of clothing from the time have things like strong reds, blues and even purer whites and greens with the higher ranking, and anyone with a bit of money for social climbing. That isn't to say the poor folks would be stuck with just browns, off-whites etc.
There is also a matter of tastes. Alot of the Danes loved Red, so they used that alot. the Irish loved purples (green for the Irish is a weird modern thing.. Hell, in old traditions, leprechauns wore Red, until more recent times when it was changed to Green.
In more modern times, around 500AD, the French royal family used Blue (Royal blue) as a ranking colour to show the king, which was thus used for the King's Guard's uniform, the Musketeers, and even up to WW1, until the days of the need for Camouflage. Much more modern, we have a weird indigo colour which is called Saxon Blue, but that was 1700s.
While my knowledge isn't 100% of course, soo many cultures used and still use Blue for a richer classes. In fantasy, do what ever you like, But historically, It wasn't a huge colour for the peasants for quite some time. Like I said, I'm more coming at this from an Anglo-Saxon point, after the Saxon's have come to England and started to mix, but before the arrival of the Normans, who would have suppressed Blue for the lower classes as they have it still firmly for their royals.
Of course, I'm still not a HUGE expert. I know Woad trade became a big thing for a while, till it was replaced, but again, lower grades wouldn't have access to alot and well, atleast these days, it's a really rare plant in the UK. How common it would have been else where, short of from trading (Vikings had a trade in it I believe) I'm not sure.
So, that's basically why I think of it more as a rich boye colour and interesting choice if you are aiming for more historically accurate. But I'll be interested if people know a bit more on the history of early Medieval dying and textiles.